The present invention concerns a bearing bush for supporting an end of a shaft.
Various apparatuses such as more particularly anchoring arrangements for freight material in aircraft involve a requirement for a shaft to be mounted at its two ends in mutually oppositely disposed side walls such as the side wall portions of an upwardly open member, in a fashion which is as reasonably simple and inexpensive as possible. In the specific context of air freight, the above-mentioned upwardly open members form for example the base members of freight container anchors which have to be anchored by means of quick-operation securing devices in rails or bars which are let into the floor of the aircraft freight compartment.
The shaft may be mounted in the supporting walls either rotatably or non-rotatably. In the former case the shaft is rotatable relative to the walls of the member in which it is mounted while in the second case the stationary shaft rotatably supports a further element.
The crucial consideration is that such shafts and their bearings must be of such a configuration that, from the point of view of the member in which they are supported, they are capable of withstanding considerable forces, in particular in a radial direction. If for example such a shaft carries a locking bolt member which can be latched fast to secure a freight container to the floor of an aircraft freight compartment, the shaft together with its bearings must be capable of carrying forces which may be extremely high in the event of in-flight movements which differ from a horizontal flight path.
In this respect the member in which such shafts are supported should generally be as light as possible and it is therefore made for example from aluminium while its mutually oppositely disposed side walls or limbs have mutually aligned bores extending therethrough, through which the respective shaft extends in such a way that the ends thereof project only slightly or virtually not at all beyond the respective outside surface of the wall of the member. As the aluminium is too soft to support the shaft in the bores with the required level of strength, fitted into each bore is a bearing bush which consists of steel and which comprises a bush body which is of a substantially hollow-cylindrical configuration so that it has a bore extending therethrough. A radially projecting collar is disposed at one end of the bush body. The axial length of the bush body is approximately equal to the thickness of the wall of the member into which the bush is to be fitted. The inside diameter of the bore in the wall of the member in which the shaft is supported is equal to the outside diameter of the hollow-cylindrical bush body so that the bush is a press fit in the bore in the wall of the member in which the shaft is to be supported. In that arrangement the bush is pushed into the bore in the wall of the supporting member to such an extent that it bears with its projecting collar against one of the side surfaces of the wall of the member.
If now a shaft which is mounted at its two ends in that way is subjected to considerable forces in a radial direction, there is the tendency for the shaft to bend in the direction of such forces, in which case the longitudinal axes of the bearing bushes become tilted relative to the longitudinal axis of installation thereof, with deformation and enlargement of the bores in which they are accommodated. In addition the upper free ends of the limbs of the supporting member tend to move away from or towards each other, depending on the direction of the force acting radially on the shaft. Such deformation phenomena may be so severe that either the shaft together with the bearing bushes is pulled out of the bores in which the bushes are accommodated, or the shaft has its ends pulled out of the bearing bushes.
In order to prevent those undesired effects from occurring, it was hitherto normal practical for the thickness of the limbs of the supporting member to be as large as possible. In order not to cause an excessive increase in the weight of the supporting members as a result, openings or recesses were formed in the side walls of the supporting member wherever there were no mounting bores. In regard to manufacture, that meant that either the supporting members were extruded with a large wall thickness throughout and thereafter the openings which served to save weight had to be milled out, or alternatively the only option was to cast the supporting members as individual components. However both methods of manufacture are complex and give rise to high levels of cost.